Loud-speaking telephone



I 1 4 2 0a. 11,1927. 4 (LEMMA ,6 5,82

oun SPEAKING TELEPHONE Filed Aug. 28, 1924 WITNESSES: I INVENTOR ATTORNEY I Patented Oct. 11, 19227.

'UNlTED STATES rarest QEEHQE.

CLINTON B. HANNA, F WILKINSBURG, PENNSYLVANIA, ASSIGNOB T0 NVESTING- HOUSE ELEGTBIG & MANUFACTURING COMIANY, A CORPORATION OF PENNSYIw VANIA.

noun-srnnxm'c TELEPHONE.

Ap mauoa filed August as, 1924. serial no. mecca This invention relates to sound-reproducing devices such 'as telephone receivers and loud s eakers.

In t e co-pending applications of Josep Slepian, Serial No. 734,609, filed Aug. 28,

1924, for a microphone circuit, of Joseph Slepian and myself, Serial No. 734,608, filed Aug. 28, 1924, for a sound-translating device, and of myself, Serial No. 7 34,605, filed Au 28, 1924, for a microphone, all assigned to Westinghouse Electric and Manufacturing' Company, various inventions are setforth which improve the faithfulnesswith which the current in the output of a microphone represents the sound impressed upon the instrument. One object of this invention is to provide for similar improvements in the faithfulness with which the sound from a sound-reproducing instrument rep- .resents the current impressed -upon such instrument. I

A. further object of this invention is' to provide a telephone receiver with a regenerative'device.

A further object of this invention is to compensate for the inertia and stifiness of the diaphragm in a telephone receiver.

A further object of this invention is to 'provide means, whereby the magnet actuating a telephone receiver shall be sub ect, not only to control by the signalling current, but also to a supplemental control correlated to the movement of the receiver diaphragm. A further object of this inventionv is to provide means whereby a regenerative action may be obtainedin a telephone receiver and a supplemental means whereby this reaction will be prevented from rendering the receiver unstable.

The single figure is a diagrammatic representation of the apparatus and circuits embodying the invention.

,A loud speaker or other telephonereceiving device, indicated in dotted lines, is provided with a diaphragm 1 actuated byan electromagnet 2. This electromagnet is in the output circuit of a tube 3 which is in the r second stage of an amplifier. The first stage includes a tube l.

The input of the tube 4 is supplied from thesecondary of a transforihefi, the pri- Other objects and structural details of my harmonic motion, may be represented by a ment.

mary ofwhich is connected to an source of signalling current. The source 0 signalling current is not illustrated since any source may be used. It is only necessary that the i received current shall represent the sound 6 to be reproduced.

A coil 6 is so associated with the diaphragm 1 that movement of the diaphragm causes a changing electromotive orce in the coil 6. The coil 6 is connected to the input of the tube 4 through conductors 7 and 8. In the conductor, 7 a condenser -9 and an inductor 11 are inserted, in parallel to each other. The conductors 7 and 8 are connected to the input circuit of the tube 7 I 4 on opposite sides of a resistor 12. A small inductor 13 is also included in series with the resistor 12 between said connections.

The conductor 8 includes a winding 14 which is inductively related to a winding 15 in the output circuit of the tube 3.- In the operation of the device, signalling current in the primary of the transformer 5 induces an electromotive force in the sec-' ondary which is impressedupon the grid of the tube 4." The output of this tube induces similar potential changes in the input of the tube 3 s with the usual amplifying action. The energy for the amplification is supplied by the plate battery 16. i

Theoutput of the amplifierenergizes the electromagnet 2 and causes the diaphragm -to.the inertia and the stifl'ness of the diaphragm, resonance will either be greatly reduced or eliminated altogether.

The movement of a diaphragm, being a rotating vector. If the rotating vector is a representation of the displacement a vector 90 in advance of it will represent the velocity. The acceleration will be represented by a vector 90 in advance of the velocity, that is, opposed to the displacement.

' The inertia reaction is a reaction opposed to the acceleration. It is, therefore, represented by? vector in phase wlth the d1splacee stifiness reaction is a reaction opposed to the displacement. It is, therefore, a vector in phase with the acceleration. Damping is a force opposed to the velocity and is properly represented by a. vector 180 different in phase from the velocity vector.

All of these vector relations are familiar to those skilled in the art and all, except the last, are readily recognized as a necessary consequence of the fact that the motion of a diaphragm is'harmonic.

Damping is a force brought into existence by the velocity. Forexample, if the damping be friction, it is readily recognized that when the diaphragm is still, there is no force exerted by friction that when the daphragm moves slowly, only slight friction is present; and that when the diaphragm moves rapidly, the force exerted by friction will be great. The propriety of describing damping as a force of the same phase as the velocity, but

' opposed in direction to it, will, therefore, be

evldent. The general, as opposed to technical use" of the term damping, makes it apply to any force which, in any way, tends to bring the diaphragm to rest. In this specification and m the claims damping is used, not in its general sense, but in its technical sense.

At low frequencies, the predominating reaction is that due to stiffness. Also, at low fre uencies, the reactanceof thecondenser 9 is t e predominating factor in the circuit 78. At high frequencies the mass has a greater effect than the stiifness; Also, at high frequencies, the reactance of the inductor 11 is the redominating element in the circuit 7-8. Kt the resonance frequency the reactions due to stiffness and inertia very largely compensate each other. At this frequency, therefore, it is undesirable that energy from the coil 6 be delivered to the grid circuit of the tube 4.

The delivery of energy from the diaphragm back to the control circuit may properly be called regeneration. At the resonance frequency, regeneration is prevented f because, for this fr uency, the .parallel conneetion including t e condenser 9 and the inductor 11, is resonant. Regeneration is, therefore, prevented at the very frequency Where it is undesired.

At other frequencies, an electromotive force is introduced across the resistor 12 and the inductor 13. The'phase of this electromotive force must be such that, at all times, it so corrects the electromotive force from the secondary of the transformer 5 that the potential impressed upon the grid of the tube 4 is mo 'fied to compensate for the reactions in the diaphragm.

The impedance of the inductor 13 -is very small as compared with that of the resistor fthe reactances of condenser 9, inductor 12. It does, however, produce a slight effect upon the phase of the correction just mentioned. This effect is needed because the acceleration of the diaphragm is not strictly in phasewith the current in the coil 2, and the electromotive force generated in the coil 6 is not strictly in phase with the velocity of the diaphragm. The lead of the electromotive force across the impedance 12-13,

phragm 1, they are in ordinary construc tions incompletely shielded from each other. There is some slight coupling between them. To compensate for the effect of such coupling upon the phase of the above-mentioned correction, the transformer let-15 is intro duced.

While I have shown only one embodiment of my invention in the accompanying drawlllgS, it is capable of various changes and modifications without depart' from the spirit thereof, -and it is desire therefore, that only such limitations shall be imposed thereon as are required by the prior art or indicated in the appended claims.

I claim as my invention:

1. In a sound-producing device, a diaphragm, magnetic driving means for said diaphragm, and means controlled by the movement of said diaphragm for impressing on said magnetic driving means a supplemental current of a phase in quadrature with the velocity of said dia hragm.

2. In a sound-repro ucing device, a. diaphragm, a signal circuit, an amplifier having an input circuit, a. driving means for said diaphragm, said amplifier having an output circuit solely energizing said driving means, means for impressing on the input circuit of said amplifier an electromotive force corresponding to the movement of saiddiaphragm, and means ,for so determining the phase of said electromotive force that the reactions duetostifiness and inertia of the diaphragm are counteracted, the phase of said electromotive force being such that the component thereof tendingv to produce damping is small relative to either of said reactions.

In testimony whereof, I- have hereunto gust 1924. c r

. CLINTON R. HANNA.

' subscribed my name this 22nd day pf Au- 

